Wheat flour is ideal for a variety of processes, such as, bread making, since the storage proteins of wheat form a strong, cohesive dough that retains gas bubbles, such as carbon dioxide produced by yeast during rising of bread products, to produce light baked products. The wheat proteins may be isolated from wheat flour by removing starch and albumins/globulins by gently working the dough under a stream of water. After washing, a rubbery ball remains comprising the wheat gluten proteins, which are known as “vital wheat gluten”. Traditionally, plant proteins have been classified into four families according to their solubility: albumins, which are soluble in water or dilute salt solutions and are coagulated by heat; globulins, which are insoluble in pure water but soluble in dilute aqueous salt solutions and insoluble in concentrated aqueous salt solutions; prolamins, which are soluble in aqueous alcohol; and glutelins, which are soluble in dilute acid or bases, detergents, or dissociating or reducing agents, such as urea or 2-mercaptoethanol, respectively.
The prolamins are considered to be unique to the seed of cereals and other grains or grasses. The prolamins have been given different names in different cereals, such as: gliadin in wheat, avenins in oats, zeins in maize, secalins in rye, and hordein in barley. The gliadins and glutenins of wheat are the storage proteins of the wheat endosperm. Gluten can be described as having a composition of gliadin and glutenin. Gluten composition is a major factor in determining wheat dough mixing strength and processing characteristics.
Gliadin, or the gliadin fraction of gluten, has a low ionic strength and excellent film forming properties. Gliadin is insoluble in water; however, its solubility may be modified with the addition of a surfactant and/or adjustment of the pH. Gliadin may absorb up to twice its weight of water. Glutenin, or the glutenin fraction of gluten, is highly elastic and rubbery and is also resistant to shear. Glutenin is insoluble in alcohol and neutral water, however, its solubility may be modified with the addition of a surfactant and/or adjustment of the pH. The protein structure of glutenin is stabilized by interchain disulfide bonds.
Vital wheat gluten is approved by the U.S. Food and Drug Administration as Generally Recognized as Safe (GRAS) under 21 C.F.R. §184.1322 for use as a dough strengthener, formulation aid, nutrient supplement, processing aid, stabilizer and thickener, surface finishing agent, and texturizing agent at levels not to exceed current good manufacturing practice. Vital wheat gluten is defined as a viscoelastic gluten that is extensible when hydrated.
Through further removal of non-protein constituents, the protein content of vital wheat gluten can be increased. The functional properties of this protein can be modified through the use of acids, reducing agents, phosphates, enzymes, and combinations thereof to convert the proteins to a “wheat protein isolate” or a “modified wheat protein isolate” (which in certain markets may be known as “hydrolyzed wheat protein”).
Wheat protein isolates may be modified with a reducing agent, such as, for example, sodium metabisulfite, bisodium sulfite, other salts of sulfite, bisulfite and/or metabisulfite, and/or other sulfur containing reducing agents. Reducing agents are added to the wheat protein isolates to cleave the inter- and/or intra-strand cross-links between protein strands, which results in a product having a lower viscosity or a more “liquid” product. However, the presence of sulfites or other sulfur containing reducing agents may result in an allergic response in certain consumers. In addition, in certain markets the presence of added sulfites in a product may preclude the use of certain descriptors, such as “natural” or “organic”, from being used to describe a product containing sulfites or a product containing a wheat protein isolate containing sulfites.
Wheat protein isolates have been used in the food industry as an ingredient to alter texture and enhance taste and appearance in food products. Wheat protein isolates may add certain benefits to food products, including, for example, replacing sugar or carbohydrate functionalities in baked or processed foods; building structure or improving crumb texture in baked goods; improving freeze-thaw performance with improved texture and mouthfeel; replacing sugar as a binder in bars and coatings for cereals; increasing protein levels in foods without sacrifice of taste and texture; improving dough rheology, proofing times, and sheeting performance; reducing fat in food products; generation of foam and other types of controlled air entrapment; and improving taste and texture in whole grain applications.